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Environmental fate & pathways

Hydrolysis

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Reference
Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 111 (Hydrolysis as a Function of pH)
Version / remarks:
adopted May 12, 1981
Qualifier:
according to guideline
Guideline:
EU Method C.7 (Degradation: Abiotic Degradation: Hydrolysis as a Function of pH)
Version / remarks:
December 1992
GLP compliance:
yes
Radiolabelling:
no
Analytical monitoring:
yes
Details on sampling:
After incubation 50 µl aliquots of the test solutions at each pH value were analysed without dilution by measuring the UV/VIS-signal of Red Rwa 4565 after HPLC separation of the injected sample solution.
Buffers:
- pH: 4.0, 7.0 & 9.0
- Composition of buffer:
Buffer pH 4, Biphthalate (Art. 5657 - Baker)
Buffer pH 7, Phosphate (Art. 5656 - Baker)
Buffer pH 9, Borate (Art. 7145 - Baker)
The buffer solutions were sterilized for 25 minutes in an autoclave prior to first use. Nitrogen was passed through the buffer solutions for 5 minutes except when freshly sterilized.
Details on test conditions:
TEST SYSTEM
- Type, material and volume of test flasks, other equipment used: All glassware, which must be inert in the pH range applied, were rinsed with sterile buffer. The hydrolysis was carried out in flasks which were stoppered or sealed with an inert material (e.g. PTFE).
- Sterilisation method: The buffer solutions were sterilized for 25 minutes in an autoclave prior to first use. Nitrogen was passed through the buffer solutions for 5 minutes except when freshly sterilized.

TEST MEDIUM
- Volume used/treatment
- Kind and purity of water:
- Preparation of test medium: The test item was dissolved in an aqueous solution at a specific pH-value (pH 4.0, 7.0 and 9.0) and was incubated at a specific temperature (in a water bath thermostated at the 50'C with a maximum deviation of t 0.5'C and then kept constant within f 0.1 'C). The concentration (at pH a.0) or the measured test item peak area (at pH 7.0 and pH 9.0) were determined as a function of time, using a suitable analytical method. ln case of decreasing concentrations, the logarithms of the concentrations are plotted against time (log1o (c,)). lf the plot is a straight line, the reaction is considered to be of (pseudo-) first order. The rate constant and the half-live time is then calculated using the slope. Otherwise, the rate constant can be estimated by the use of the Arrhenius relationship.

Preparation of the Test Solutions

Hydrolysis at 50°C

-pH 4.0, Preliminary Test and Main test
11.44 mg of Red Rwa 4565 were dissolved in 100 ml buffer solution (pH a.0) with aid of sonication to prepare a test solution of 114.4 pg/ml. This solution was filtered (0.2 pm) and two aliquots of this test solution of approximately 50 ml each were transferred into 50 ml Erlenmeyer flasks in order to perform a duplicate test.

-pH 7.0, Preliminary Test
11.32 mg of Red Rwa 4565 were dissolved in 100 ml buffer solut¡on (pH 7.0) to prepare a test solution of 1 13.2 pglmL Two aliquots of this test solution of approximately 50 ml each were transferred into 50 ml Erlenmeyer flasks in order to perform a duplicate test. After 24 hours of incubation at 50'C, the components of the test item decomposed such as just one peak was visible in the HPLC chromatogram. The hydrolysis behaviour of this peak was followed.

-pH 9.0, Preliminary Test
9.64 mg of Red Rwa 4565 were dissolved in 100 ml buffer solution (pH 9.0) with aid of sonication to prepare a test solution of 96.4 pg/ml. This solution was filtered (0.2pm) and two aliquots of this test solution of approximately 50 ml each were transferred into 50 ml Erlenmeyer flasks in order to perform a duplicate test.

-pH 9.0, Main Test
13.43 mg of Red Rwa 4565 were dissolved in 100 ml buffer solution (pH 9.0) to prepare a test solution of 134.3 pg/ml. Two aliquots of this test solution of approximately 50 ml each were transferred into 50 ml Erlenmeyer flasks in order to perform a duplicate test. After 4 hours of incubation at 50 'C, the components of the test item decomposed such as just one peak was visible in the HPLC chromatogram. The hydrolysis behaviour of this peak was followed.

Hydrolysis at 50°C

-pH 4.0, Main Test
12.47 mg of Red Rwa 4565 were dissolved in 100 ml buffer solution (pH a.0) to prepare a test solution of 124.7 pgtmL Two aliquots of this test solution of approximately 50 ml each were transferred into 50 ml Erlenmeyer flasks in order to perform a duplicate test.

-pH 9.0, Main Test
12.11 mg of Red Rwa 4565 were dissolved in 100 ml buffer solution (pH 9.0) to prepare a test solution of 121.1 pgtmL Two aliquots of this test solution of approximately 50 ml each were transferred into 50 ml Erlenmeyer flasks in order to perform a duplicate test. After 0.5 hours of incubation at 70'C, the components of the test item decomposed such as just one peak was visible in the HPLC chromatogram. The hydrolysis behaviour of this peak was followed.

Hydrolysis at 80'C

-pH 4.0, Main Test
13.92 mg of Red Rwa 4565 were dissolved in 100 ml buffer solution (pH a.0) to prepare a test solution of 139.2 pg/ml. Two aliquots of this test solution of approximately 50 ml each were transferred into 50 ml Erlenmeyer flasks in order to perform a duplicate test.

-pH 9.0, Main Test
11.00m9 of Red Rwa 4565 were dissolved in 100 ml buffer solution (pH 9.0) to prepare a test solution of 110.0 pg/ml. Two aliquots of this test solution of approximately 50 ml each were transferred into 50 ml Erlenmeyer flasks in order to perform a duplicate test. After 20 minutes of incubation at 80 'C, the components of the test item decomposed such as just one peak was visible in the HPLC chromatogram. The hydrolysis behaviour of this peak was followed.
Duration:
5 d
pH:
4
Temp.:
50 °C
Initial conc. measured:
101.62 - 108.36 other: µg/ml
Remarks:
preliminary test
Duration:
5 d
pH:
7
Temp.:
50 °C
Initial conc. measured:
3 991 108 - 4 418 591 other: peak area
Remarks:
preliminary test
Duration:
5 d
pH:
9
Temp.:
50 °C
Initial conc. measured:
3 984 936 - 4 367 024 other: peak area
Remarks:
preliminary test
Duration:
5 d
pH:
4
Temp.:
70 °C
Remarks:
Half-time
Duration:
3 d
pH:
4
Temp.:
80 °C
Remarks:
Half-time
Duration:
195 d
pH:
4
Temp.:
25 °C
Remarks:
Half-time
Duration:
3 h
pH:
9
Temp.:
70 °C
Remarks:
Half-time
Duration:
1 h
pH:
9
Temp.:
80 °C
Remarks:
Half-time
Duration:
32 d
pH:
9
Temp.:
25 °C
Remarks:
Half-time
Number of replicates:
2
Positive controls:
no
Negative controls:
no
Statistical methods:
Not used
Transformation products:
not measured
pH:
4
Temp.:
25 °C
Hydrolysis rate constant:
0 h-1
DT50:
4 687 h
Type:
(pseudo-)first order (= half-life)
pH:
4
Temp.:
50 °C
Hydrolysis rate constant:
0 h-1
DT50:
538 h
Type:
(pseudo-)first order (= half-life)
pH:
4
Temp.:
70 °C
Hydrolysis rate constant:
0.005 h-1
DT50:
127 h
Type:
(pseudo-)first order (= half-life)
pH:
4
Temp.:
80 °C
Hydrolysis rate constant:
0.012 h-1
DT50:
60 h
Type:
(pseudo-)first order (= half-life)
pH:
9
Temp.:
25 °C
Hydrolysis rate constant:
0.001 h-1
DT50:
759 h
Type:
(pseudo-)first order (= half-life)
pH:
9
Temp.:
50 °C
Hydrolysis rate constant:
0.023 h-1
DT50:
31 h
Type:
(pseudo-)first order (= half-life)
pH:
9
Temp.:
70 °C
Hydrolysis rate constant:
0.217 h-1
DT50:
3 h
Type:
(pseudo-)first order (= half-life)
pH:
9
Temp.:
80 °C
Hydrolysis rate constant:
0.589 h-1
DT50:
1 h
Type:
(pseudo-)first order (= half-life)
Details on results:
HYDROLYSIS AT 50.0°C

pH 4.0
At this pH value the parallel degradation of four main peaks was followed. The results of the preliminary test show, that Red Rwa 4565 is not stable at pH 4.0. Therefore the test at 50 "C was extended in the range of 20% to 70 % degradation. The linear plots prove that the hydrolysis reaction is of pseudo first order in the range from 20 o/o to 70 % hydrolysis at pH 4.0, The reaction rate constant k for pH 4.0 was calculated by regression analysis. The half-life time of Red Rwa 4565 at 50.0°C and pH 4.0 was calculated to be 538 hours (22 days).

pH 7.0
At pH 7.0 the degradation of the resulting fourth peak was followed. The peak followed at pH 7.0 showed no significant degradation (degradation lower than 10%) of Red Rwa 4565 at 50°C. According to the EEC Directive 92169, Section C.7, it can be concluded, that the estimated half-life time is higher than one year under representative environmental conditions (25 °C). Therefore, the fourth main component of Red Rwa 4565 can be considered to be hydrolytically stable at pH 7.0 and no further testing was necessary at this pH-value.

pH 9.0
At pH 9.0 the degradation of the resulting fourth peak was followed. The results of the preliminary test show, that the fourth main component of Red Rwa 4565 is not stable at pH 9.0. Therefore the test at 50 °C was repeated in the range of 20 % to 70 % degradation. The linear plots prove that the hydrolysis reaction is of pseudo first order in the range from 20 % to 70 % hydrolysis at pH 9.0. The reaction rate constant k for pH 9.0 was calculated by regression analysis. The half-life time of the fourth main component of Red Rwa 4565 at 50.0 'C and pH 9.0 was calculated to be 31 hours.

HYDROLYSIS AT pH 4.0 AND DIFFERENT TEMPERATURES

Calculation of the Half-Life Time at pH 4.0
The further hydrolysis tests at pH 4.0 were performed at 70°C and 80°C, each in duplicate. Each buffered test solution was analysed in time intervals. The obtained linear plot of each sample prove that the hydrolysis reaction is pseudo first order at 70 °C and 80 °C. The half-life time at pH 4.0 and 70 °C was calculated to be 127 hours (5 days). The half-life time at pH 4.0 and 80 °C was calculated to be 60 hours (3 days).

Evaluation of the Half-Life Time at 25 °C
The half-life time of the hydrolysis reaction of Red Rwa 4565 al 25 "C and pH4.0 was calculated to be 4687 hours (195 days).

HYDROLYSIS AT pH 9.0 AND DIFFERENT TEMPERATURES

Calculation of the Half-Life Time at pH 9.0
The further hydrolysis tests at pH 9.0 were performed at 70°C and 80°C, each in duplicate. Each buffered test solution was analysed in time intervals. The obtained linear plot of each sample prove that the hydrolysis reaction is pseudo first order at 70 °C and 80 °C. The half-life time at pH 9.0 and 70 °C was calculated to be 3 hours. The half-life time at pH 9.0 and 80°C was calculated to be 1 hour.

Evaluation of the Half-Life Time at 25 °C
The half-life time of the hydrolysis reaction of Red Rwa 4565 al 25'C and pH 9.0 was calculated to be 759 hours (32 days).
Results with reference substance:
none
Validity criteria fulfilled:
yes
Conclusions:
The fourth main peak of Red Rwa 4565 was found to be stable at pH 7.0 and 50 °C. Therefore no further testing was performed at this pH-value. lts half-life time is longer than one year at 25 °C.
Red Rwa 4565 at pH 4.0 has a half-life time of 4687 hours (195 days) at 25 °C.
The fourth main component peak of Red Rwa 4565 at pH 9.0 has a half-life time of 759 hours (32 days) at 25 °C.
Executive summary:

The hydrolysis determination of Red Rwa 4565 at different pH values was based on the OECD Guideline No. 111, "Hydrolysis as a Function of pH"; adopted May 12, 1981 and on the EEC Directive 92/69, Section C.7, "Abiotic Degradation: Hydrolysis as a Function of pH", L383 A, December 1992.

The hydrolysis of the test item was performed at 50.0'C t 0.1 "C at each of pH 4.0, pH 7.0 and pH 9.0. The degradation behaviour of Red Rwa 4565 varies at different pH values. At pH 4.0 all four test item peaks degrades parallel. During the degradation, the sum of four test item peaks was followed. At pH 7.0 and pH 9.0 a different degradation behaviour was observed. At this pH value three test item peaks degrades to one peak. The degradation of this emerging peak was followed. The emerging peak is the last of the four main component peaks of Red Rwa 4565 with a retention time of about 15 minutes.

The fourth main peak of Red Rwa 4565 was found to be stable at pH 7.0 and 50 °C. Therefore no further testing was performed at this pH-value.

Red Rwa 4565 was not stable at pH 4.0 and at pH 9.0, further testing was performed at elevated temperatures in order to calculate the rate constant (kru) and the half-life time of the

hydrolysis at pH 4.0 and at pH 9.0 at 25 "C. The results are summarised below (the values typed in italics were calculated using the Arrhenius equation):

 pH  Temperature [°C]  Reaction rate constant k [1/hours]  Reaction rate constant k [1/s]  Half-life time t 1/2 [hours]
4.0  25  1.48E-4  4.11E-8  4687
 50  1.29E-3  3.58E-7  538
 70  5.49E-3  1.53E-6  127
 80  1.16E-2  3.22E-6  60
9.0  25  9.13E-4  2.54E-7  759
 50  2.27E-2  6.31E-6  31
 70  2.17E-1  6.03E-5  3
 80  5.89E-1  1.64E-4  1

The fourth main component peak of Red Rwa 4565 is stable at pH 7.0. lts half-life time is longer than one year at 25 °C.

Red Rwa 4565 at pH 4.0 has a half-life time of 4687 hours (195 days) at 25 °C.

The fourth main component peak of Red Rwa 4565 at pH 9.0 has a half-life time of 759 hours (32 days) at 25 °C.

Description of key information

The hydrolysis determination of Red Rwa 4565 at different pH values was based on the OECD Guideline No. 111, "Hydrolysis as a Function of pH"; adopted May 12, 1981 and on the EEC Directive 92/69, Section C.7, "Abiotic Degradation: Hydrolysis as a Function of pH", L383 A, December 1992.

The fourth main peak of Red Rwa 4565 was found to be stable at pH 7.0 and 50 °C. Therefore no further testing was performed at this pH-value. lts half-life time is longer than one year at 25 °C.

Red Rwa 4565 at pH 4.0 has a half-life time of 4687 hours (195 days) at 25 °C.

The fourth main component peak of Red Rwa 4565 at pH 9.0 has a half-life time of 759 hours (32 days) at 25 °C.

Key value for chemical safety assessment

Additional information